A power factor correction (PFC) converter is an essential component of power converter structures that derive power from an alternating current (AC) source such as the power distribution network or grid. The power factor correction function serves to prevent phase changes due to variation in load current from being reflected to the AC source and to maintain high efficiency by insuring that power is transferred to a load substantially in phase with the instantaneous voltage provided by the AC power source. This function is generally accomplished by switching that is varied in frequency and/or duty cycle with the magnitude of the voltage provided by the AC power source.
There are several trade-offs in the design of physical PFC converters, particularly in regard to efficiency, filtering of switching noise and power density (e.g. the amount of power that can be provided to a load per unit of volume of the PFC converter). In general, a nominal (or minimum) operating frequency is chosen to be in a range below several hundred KHz. At such switching frequencies, the PFC converter component requires about one-third of the volume of an AC/DC converting power supply for the necessary switches, EMI switching noise filter, inductors and filter capacitor to provide power factor correction. Increasing the switching frequency can reduce the volume of a PFC converter and raise the corner frequency of the EMI filter and PFC converter to reduce overall power converter size. However, increased switching frequency substantially increases switching power losses, particularly due to the high turn-on losses for cascade gallium nitride (GaN) devices currently preferred for high power applications. Such high turn-on losses can be overcome by a critical conduction control method (CRM) in which switches are controlled to draw power from a source when inductor current reaches zero and turned off a fixed time later which is preferred for that reason and referred to as constant on-time (COT) control. Additionally, losses due to reverse recovery of the power diode in a CRM boost PFC converter may be reduced through use of zero current switching (ZCS). Higher possible power factor and reduced peak inductor current are other advantages that can be obtained from a CRM boost PFC converter. Unfortunately, the topology of a boost PFC converter is complex and, hence, more expensive to produce than other PFC converter topologies.
For example, a so-called totem-pole PFC converter is far simpler than a boost converter or other bridgeless PFC converter topologies. While totem-pole topologies were not practical in the past due to the reverse recovery performance of the body diodes of switches included therein, that problem is ameliorated with GaN switches currently available; increasing interest in this simplified topology. However, several intractable problems with the totem-pole PFC converter topology remain: large frequency excursions during half-cycles of the input line frequency AC voltage and the inability to achieve zero voltage switching over the entirety of an input voltage half-cycle; both of which engender large losses and limit efficiency.
The concept of using coupled inductors has been widely applied in multiphase voltage regulator modules (VRMs, as distinct from PFC converters) to limit losses and improve transient response. The concept of coupled inductors has also been evaluated in interleaved CRM boost PFC converters. However, no solution to the frequency excursion and problems in achieving ZVS switching in totem-pole PFC converters have been previously found. Additionally, in interleaved multiphase PFC converters with coupled inductors, the input current ripple, which has an impact on differential mode (DM) noise, is determined by the leakage inductance of the coupled inductor and, since the leakage inductance is smaller than the leakage inductance of the non-coupled inductors, the DM noise will be larger. Reduction of common mode (CM) noise by balancing techniques in some types of power converters is also known. However, it is not known if balancing techniques can be applied to reduce or eliminate CM noise problems in totem-pole PFC converters or if suitable balancing techniques are consistent with compact coupled inductor structures, especially of the PCB winding type.